Veritas R8 making loud tizzing noise, what could cause this?

The control panel of our veritas R8 has started making a loud tizzing noise, if I press on the panel cover it goes away but come back low and slowly gets louder when I stop pressing. The green light on the panel is on & stable. All functions of the system seem to be working ok. Have taken cover off and when hold battery the noise stops, does this mean the back up battery is on its way out? Thanks for any ideas